<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            height: 200px;
            background-color: green;
            /* display: none; */
            opacity: 0;/*transition 过度效果 */
            /* visibility: hidden; */
            /* position: absolute;
            z-index: -9999; */
            /* transform: scale(0); */
        }
        /* .container{
            height: 0;
            overflow: hidden;
        } */
        .box:hover{
            opacity: 1;
            transition: opacity 5s;
        }
    </style>
</head>
<body>
    <!-- <div class="container"> -->
        <div class="box"></div>
        ddddd
    <!-- <div class="box"></div> -->
</body>
</html>